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For further information, see CMDT Part 13-31: Hairy Cell Leukemia

Key Features

Essentials of Diagnosis

  • Pancytopenia

  • Splenomegaly, often massive

  • "Hairy" cells present on blood smear and especially in bone marrow biopsy

General Considerations

  • Malignancy of hematopoietic stem cells differentiated as mature B-lymphocytes with "hairy" cytoplasmic projections

  • V600E mutation in the BRAF gene

    • Recognized as the causal genetic event of hairy cell leukemia

    • Detectable in almost all cases at diagnosis and present at relapse

  • Rare


  • Characteristically presents in middle-aged men

  • Median age at presentation is 55 years

  • Striking 5:1 male predominance

Clinical Findings

Symptoms and Signs

  • Gradual onset of fatigue

  • Symptoms related to markedly enlarged spleen

  • Splenomegaly is almost invariably present and may be massive

  • Increased susceptibility to infection

  • Hepatomegaly in 50% of cases

  • Lymphadenopathy uncommon

Differential Diagnosis

  • Myelofibrosis

  • Chronic lymphocytic leukemia

  • Waldenström macroglobulinemia

  • Non-Hodgkin lymphoma

  • Aplastic anemia

  • Other cause of bone marrow infiltration, eg, metastatic cancer, infection


Laboratory Tests

  • Complete blood count

    • Pancytopenia

    • Anemia nearly universal

    • Thrombocytopenia and neutropenia in 75% of patients

  • Peripheral blood smear: "hairy cells," with numerous characteristic cytoplasmic projections, may be present in small numbers

  • Hairy cells coexpress CD11c, CD20, CD22, CD25, CD103, and CD123 on immunophenotyping

Diagnostic Procedures

  • Bone marrow aspirate: often inaspirable (dry tap)

  • Bone marrow biopsy establishes diagnosis made by characteristic morphology

  • Pathologic examination of spleen shows marked infiltration of red pulp with hairy cells (in contrast to usual predilection of lymphomas to involve white pulp)



  • Single course of pentostatin or cladribine

    • Treatment of choice

    • Median duration of response is over 8 years and patients who relapse a year or more from their initial therapy can be treated again with one of these agents

    • Treatment is associated with infectious complications and patients should be closely monitored

  • Rituximab can be used in the relapsed setting either as a single agent or in combination with a nucleoside analog

  • Vemurafenib, BRAF inhibitor

    • Exhibits ~100% overall response rate in patients with refractory/relapsed hairy cell leukemia, with 35–40% complete remissions

    • Median relapse-free survival is ~19 months in patients who achieved complete remission and 6 months in those who obtained a partial response

  • Moxetumomab pasudotox

    • A recombinant CD22-targeting immunotoxin approved for patients with refractory disease

    • Has shown a durable complete response rate of 31% in the pivotal trial

    • However, it can be associated with capillary leak and hemolytic-uremic syndrome attributable to the diphtheria toxin moiety

  • See Table 39–3

Table 39–3.Common cancer therapeutic agents.

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